NUMERICAL SIMULATION ON THE FIREPROOF BEHAVIOR OF RC BEAM STRENGTHENED WITH STRANDED MESH AND POLYMER MORTAR

Transcription

1 1 NUMERIAL SIMULATION ON THE FIREPROOF BEHAVIOR OF R BEAM STRENGTHENED WITH STRANDED MESH AND POLYMER MORTAR M.G. Yue 1, Q.L. Yao, Y.Y. Wang and H.N. Li 1 State Key Laboratory of otal and Offhore Engineering, Dalian Univerity of Tehnology, Dalian hina Intitute of Earthquake Engineering, hina Aademy of Building Reearh, Beijing hina ymg008@16.om ABSTRAT : The new trengthening tehnology by uing high trength material of tranded meh and polymer mortar (SMPM) employ advantage in omparion with traditional one, and preent tudie are mainly fouing on trength inreaing of member. In thi paper, numerial imulation on fireproof behavior of R beam trengthened by SMPM i arried out with ABAQUS program, in whih the oupled proe of temperature and diplaement i fully onidered, and the real irumtane of fire expoing in a large tove i reprodued. The alulating formula of thermal ondutivity and peifi heat apaity are propoed by analyzing the thermophyial harateriti of the polymer mortar. Variation in defletion at pan enter and etion temperature of the trengthened beam under tandard temperature-time urve i alo imulated. Variation in etion temperature of beam in alulation i loely mathed to the tet. Defletion of pan enter in both experiment and numerial imulation reah to 190mm when fire loading lat 10min, whih i below the maximum allowane limit regulated by Fireproof ode of Building (L/0, 55mm for the beam). Therefore, the new trengthening method an atify fireproof requirement no need to take any other meaure. KEYWORDS: Strengthening; Stranded Meh and Polymer Mortar (SMPM); fireproof behavior; numerial imulation; ondutivity oeffiient; peifi heat 1. INTRODUTION Strengthening with high trength material of tranded meh and polymer mortar (SMPM) i a new tehnology propoed by Korea firt. In the pat few year, the reearh and development of dometi material with independent intelletual property right have been done by hina Aademy of Building Reearh (ABR). The tehnology ha peial advantage ompared with other traditional one, however, majority of preent tudie are fouing on trength inrement of truture omponent and little on the other performane harateriti (Yue M.G. 007, Yao Q.L. 005 and Nie J.G. 005). So in thi paper a numerial imulation on the fireproof behavior of R beam trengthened by SMPM i arried out with ABAQUS program on the bai of previou experiment (Wang Y.Y. 007).. FINIT ELEMENT MODEL.1 Introdution of the Fireproof Experiment (Wang Y.Y. 007, GB/T and GB ) At the beginning, a brief introdution of the fireproof experiment i preented. A imply upported beam i deigned with total length of 5.7m in experiment. The effetive length of the beam in alulation i 5.1m and the ro-etion i 00mm 350mm. The grade of onrete i 0 and the overing thikne i 5mm. The fore bearing reinforement at the beam bottom i 16 and the upporting rebar at the top i 10, and the tirrup arrangement i φ8@100/00. The beam i trengthened with tranded meh and polymer mortar and the peifiation of tranded meh i φ3.05@30, and the overing thikne of trand i about 13mm. Four onentrated fore are applied at 1/8, 3/8, 5/8 and 7/8 of beam length and the fore value i gradually inreaed to 80% (10.5kN at eah poition) of the trengthened beam bearing apaity by 5 tep. There hall be a 10min interval between eah tep. The fire load tart up when the dead load ompletely applied, and dead load hould remain unhanged until the tet end. The temperature of the tove hall aord with the tandard

2 temperature urve. The maximum defletion at pan enter reahe to 191.5mm while the fire loading lat for 10min, whih i below the maximum allowane limit regulated by Fireproof ode of Building L/0, that i, 55mm for the beam.. Etablihing the Finite Element Model Aording to the beam parameter in experiment, the finite element model i etablihed with ABAQUS proedure. The onrete and mortar are modeled in one part with olid element firt of all and then material property i aigned to different portion. The reinforing age of the rebar and trand i modeled in another part with tru element. The next tep i to ombine the two together at proper poition by the ommand embedded whih an imulate the tiking and lipping between onrete and reinforement perfetly. The finite element model i etablihed by now, ee figure 1. Fig. 1 Finite element model of R beam The load in imulation i onitent with the experiment that inlude dead load and fire load. The loading proe i divided into 3 tep, the firt tep gravity load of the beam added, the eond tep i the four onentrated fore, the initial value of whih i et to very mall in order to onverge eaily and then gradually inreae to the preet value, in the finally tep, fire load i applied aording to the urve of tandard temperature while the dead load remaining unhanged and the time of thi tep i 10min. 3. THERMOPHYSIAL AND THERMODYNAMIAL HARATERISTIS The phyial and dynami harateriti of rebar, onrete and mortar may be hanged under high temperature aount for the variation in phyial parameter. The fireproof harateriti of material an be refleted in two apet: a) phyial harateriti of material for the temperature field alulation of truture omponent, inluding thermal expanion oeffiient, heat-tranfer ondutivity, peifi heat and denity et. b) dynami harateriti of material for the internal fore and defletion alulation, and alo for fireproof harateriti heking, inluding young modulu, trength, ontitutive relationhip of train and tre, train relaxation and reeping et. ompared with the other parameter, the expanion oeffiient and denity of the material have little enitivity to temperature and mall affetion to temperature tre, o they are negleted in numerial imulation. In addition, only taking hort-term fire loading into onideration, therefore the affetion of train relaxation and reeping of reinforement are alo negleted. The variation rule of material harateriti of trand at high temperature i approximately onidered the ame a reinforement. 3.1 harateriti of Reinforement and Strand at High Temperature a) Heat-tranfer ondutivity of general teel i aording to E3 (1993) and E4 (1994):

3 T 0 T 800 λ = < T 100 (3.1) λ refer to heat-tranfer ondutivity of teel (W/(m )) and T refer to teel temperature. b) The exat formula for peifi heat alulation in manual ompiled by BSI (1990) i adopted in thi imulation: = + T + T T (3.) refer to peifi heat of general teel (J/(kg )) and T refer to temperature. ) The redution fator of young modulu and trength of general truture teel at high temperature are preented in table 1 and aording to E3 (1993): Table 1 Young modulu redution fator of truture teel at high temperature (E T /E) Temperature ( ) oeffiient Table Material trength redution fator of truture teel at high temperature (f yt /f y ) Temperature ( ) Total Strain harateriti of onrete at High Temperature A erie of phyial and hemial variation in onrete omponent will happen at high temperature and may affet the harateriti of onrete. Some reearhe indiate that onrete may hrink and the keletal material may expand a portion free water and gel water evaporate when temperature below 300 ; when temperature reahe to 400, the gel of -S-H beome looe and ome a(oh) tart deompoe; when temperature reahe to 500, the onrete ha been dehydrated ompletely, the onrete lurry hrink harply and keletal material expand ontinuouly, o large internal tre may generate and the tiking urfae inide may be damaged, at the ame time, a great deal of a(oh) begin to deompoe; when temperature reahe to 700, the onrete beome reidual material with looen truture, and the rak between keletal material and lurry develop quikly; when temperature reahe to 900, the limetone tart deompoe, keletal material and lurry dijointed ompletely (Lin W.M. 1996, Wu B. 1999). a) The hear-tranfer ondutivity of onrete mainly depend on it omponent, the key affetion fator inluding type of keletal material, moiture ontent and mixture ratio of onrete et. In imulation, the formula propoed by Lie and Denham (1993) i adopted: < T 93 λ = T T > 93 (3.3) λ i heat-tranfer ondutivity of onrete (W/(m )) and T i the onrete temperature.

4 b) The peifi heat of onrete will inreae with temperature and the following formula i uggeted by E4: = T + T + T (3.4) 4( /10) / i peifi heat of onrete (J/(kg )) and T i onrete temperature. ) Variation in young modulu and trength of onrete under high temperature are propoed in reearh of Guo Zhenhai and Li Wei (1991): ET, / E = T T 700 (3.5) f f = T + T (3.6) 17 u, T / u 1/(.4 ( 0) 10 1) ftt, / ft = 0.001T T 1000 (3.7) E,T E denote the onrete young modulu at high temperature and normal temperature repetively; f u,t f u denote the ompreive tre of ubi tet blok at high temperature and normal temperature; f t,t f t denote the tenile tre of ubi tet blok at high temperature and normal temperature. 3.3 harateriti of Polymer Mortar under High Temperature The polymer mortar ued in trengthening i a new material, the latex in mortar mixing i a water material without any organi olvent, o it ha perfet tiking and fireproof harateriti, however, there i no reearh on it fireproof harateriti at high temperature by now. In thi paper, baed on the variation in onrete harateriti at high temperature and the numerial imulation of variation in temperature of polymer mortar, the alulation formula of hear-tranfer ondutivity and peifi heat of polymer mortar are propoed (Eqn. 3.8 and Eqn. 3.9). ompared with onrete, the polymer mortar ha maller heat-tranfer ondutivity and larger peifi heat, o the fireproof harateriti of polymer mortar i better than onrete. A the trengthening layer generally lie in tenion area, the tenion trength of mortar ha little affetion on fore bearing apaity of truture omponent, therefore the variation in young modulu, tenion trength and ompreion trength of polymer mortar under high temperature are aumed idential to onrete < TM 93 λm = (3.8) TM TM > 93 M = 6( TM /10) + TM TM 100 (3.9) The meaning of parameter in above formula i the ame a onrete. 4. OMPARISON BETWEEN SIMULATION AND EXPERIMENT The temperature ditribution of the trengthened beam with 3 ide expoed to fire for 10min i diplayed in figure. From whih we an alo learly ee the ro-etion meh, the outer -layer mehe of the beam are the over of reinforement exept bottom ide. At bottom, the firt 3-layer mehe are trengthening layer in whih the outer layer of meh i the over of trand, and the upward -layer mehe from trengthening layer are the over of reinforement. From the temperature ditribution, we an onlude: a) the over of reinforement i a perfet fireproof layer, in whih the temperature dereae harply from 109 to about 580 ; b) the temperature gradient in trengthening layer i larger than in reinforement over, o the polymer mortar i better in fireproof. The omparion between imulation and experiment i hown in figure 3, inluding temperature of tirrup at middle of lateral ide, temperature of the enter trand and defletion at pan enter. The dahed line indiate

5 experiment value and the olid line denote imulation value Temperatiure ( o ) experiment-tirrup1 experiment-tirrup imulation Temperature ( o ) experiment imulation Diplaement (mm) experiment imulation Fig. Temperature ditribution at 10min Time () a) Stirrup temperature at middle of lateral ide Time () b) Temperature of the entral trand Time () ) Defletion at pan enter Fig. 3 omparion between numerial imulation and experiment In fig. 3 a) and b), the temperature variation of reinforement and trand in numerial imulation well agree with whih in experiment, therefore the proedure of ABAQUS an perfetly imulate the inner temperature ditribution of R member expoed to fire, in addition, the validity of formula in thermophyial alulation of polymer mortar, whih propoed in thi paper, i approved by the trand temperature omparion. Large differene of variation in defletion at pan enter diplayed nearly all through the proe exept at the beginning and end. In experiment, defletion inrement of beam i nearly linear and lower in the former 100min while whih i alo linear but fater in min. In numerial imulation, the defletion remain nonlinear all through the proe, and inrement i lower in 80-10min ompared with experiment. The total defletion of beam at pan enter i 193.8mm for imulation, whih approahe to experiment (191.5mm). Defletion in both imulation and experiment are below the maximum allowane limit regulated by Fireproof ode of Building L/0 (55mm). Therefore, the new trengthening method an atify the fireproof requirement without taking any other meaure (GB/T and GB ). Now we will analyze the aue for differene of defletion in experiment and imulation. Figure 13 a) indiate the temperature of reinforement approah to 500 at 80min, at the time, the burnt depth of onrete i not exeed the thikne of reinforement over, o the tiffne redution of beam ro-etion i little. On the other hand, the redution in reinforement yielding trength i alo not muh, about 0.8 time of whih at normal temperature. A a reult, the large diplaement of 130mm at 80min i impoible. The previou reearhe indiate the defletion at pan enter of imply upported beam i affeted by many fator, uh a thikne of reinforement over, dead load in fire, ize of member ro-etion. So the differene between experiment and imulation motly aued by ontrution error, inauray ontrol of oil preure (ontrol manually in experiment) and meaurement error while all the fator of imulation are in perfet tate. So the fireproof harateriti of trengthened beam in real projet may between the experiment and numerial imulation. 5. ONLUSION A to the new tehnology that trengthened with SMPM, mot tudie fou on the bearing apaity by now. However, the appraiement of a trengthening method not only on bearing apaity but alo extenively on fireproof, mitigate orroion, durability and environment protetion et. Therefore, baed on the fireproof experiment of beam trengthened with SMPM, numerial imulation with ABAQUS proedure i arried out in thi paper, ummed up the above analyi, we an onlude: The variation in temperature of trengthened beam expoed to fire an be imulated perfetly by ABAQUS proedure, whih an vividly reprodue the whole proe of beam in fire; Formula in alulation of heat-tranfer ondutivity and peifi heat of the new polymer mortar are propoed by the omparion between numerial imulation and experiment; Both the imulation and experiment indiate the new tehnique trengthened with SMPM an atify the fireproof requirement without taking any other meaure in addition other advantage, uh a inreaing member trength obviouly, onvenient ontrution, mall trengthening quantity and environment

6 protetion. The oupling of temperature filed and diplaement field an be modeled by ABAQUS proedure perfetly. The numerial imulation an not only redue the number of tet member and ave the ot but alo offet the defiieny in experiment. AKNOWLEGMENTS Greatly thank for the upport of R&D Subjet of ontrution Minitry of hina (No. 05-k4-18) and Key Seimi Tehnique Reearh and Demontration of Large and Important Building, Sub-topi of Eleventh Five-Year National Sientifi Support Plan (No ). REFERENE Yue Maoguang, Yao Qiulai and Wang Yayong et. omparion SMPM with Other Strengthening Tehnique and the Introdution of Member Strengthening Proedure. Earthquake Reitant Engineering and Retrofitting, 007, 9: 5, (in hinee) Yao Qiulai, Wang Zhonghai and Wang Yayong et. High trength teel twit wire meh-polymer mortar ompoite oating reinforement tehnique A new green reinforement tehnique. Quality of ivil Engineering and ontrution, 005, 1, 17-0 (in hinee) Nie Jianguo, Wang Hanbing and Zhang Tianhen et. Experimental tudy on flexural behavior of R beam trengthened with tainle teel wire meh and permeability polymer mortar. Journal of Building Struture, 005, 6:, 1-9 (in hinee) Wang Yayong, Yao Qiulai and Wang Zhonghai et. Fire Reitane Tet of R Beam Retrofitted with over of High Strength Steel Meh and Polymeri Mortar. Building Struture, 007, 37: 1, (in hinee) Fire-Reitane Tet-Element of Building ontrution (GB/T ), Standard Pre of hina, 1999 ode for fire protetion deign of tall building (GB ), hina Planning Pre, 1995 (in hinee) European ommittee for Standardization, ENV , Euroode 3, Deign of ompoite and onrete Struture, Part 1.; Strutural Fire Deign, 1993 European ommittee for Standardization, ENV , Euroode 4, Deign of ompoite and onrete Struture, Part 1.; Strutural Fire Deign, 1994 Britih Standard Intitution (BSI), BS 5950, the Strutural Ue of Steelwork in Building, Part 8: ode of Pratie of Fire Reitant Deign, 1990 Lin W. M., Lin T. D., Power-ouh L. J. Mirotruture of fire-damaged onrete. AI Material Journal, 1996, 93: 3, Wu Bo, Yuan Jie and Yang Qinghan. Analyi of the Mirotruture of HS after High Temperature. Journal of Harbin Univerity of ivil Engineering and Arhiteture, 1999, 3: 3, 8-1 (in hinee) Lie T. T. and Denham E. M. A., Fator affeting the fire reitane of irular hollow teel olumn filled with bar-reinfored onrete. NR-NR Internal Report, 1993, No. 651 Guo Zhenhai and Li Wei. Tet reearh on the Mehanial Behavior of onrete at Elevated Temperature.. Shool of ivil Engineering Tinghua Univerity, 1991: 9-0 (in hinee) Zha Xiaoxiong and Zhong Shantong. Nonlinear analyi of fire reitane of R bending member ubjeted to three-ide fire. J. Huazhong Univ. of Si. & Teh. (Nature Siene Edition), 00, 30: 7, 9-94 (in hinee)